The PSI UCN source Status summer/autumn 2007: 1) Introduction 2) Source principle 3) R & D experiments UCN storage, losses and depolarization UCN production in solid deuterium 4) Some impressions

Zürich - Vancouver

Switzerland PSI

Paul-Scherrer-Institut SLS: 600 MeV p cyclotron 2 mA, 1.2 MW, since 1974 Upgrade 2 MW (2009) SR:, SINQ: n UCN: n Proton cyclotron for medical application: p PSI: 1200 employees 1000 external users

Ring cyclotron: 600MeV, 2mA 1.2MW (unique!) Proton PSI UCN Source nEDM experiment

600 MeV How do we make neutrons at PSI?

PSI UCN source spallation target 1.2 MW p beam 2.5 m 2m 3

Spallationsprozess

PSI UCN source heavy water moderator 2.5 m 2m 3

PSI UCN source heavy water moderator 2.5 m 2m 3 Lebensdauer in D 2 O: 5 ms v = 2200 m/s Reichweite: ~10 m

Spallation target: lead (82p + 126n) Proton beam: 2mA (or more!) p/s 1 proton 10 neutrons n/s ~10 s Puls n/puls Average neutron energy 2MeV km/s After ca. 30 bounces ~25 meV 2200 m/s Neutron production at PSI (SINQ, UCN)

/cm 2 /mA Φ 0 Thermal flux sD2 Pb Neutron flux at PSI UCN source sD 2 near target! 8 s-puls (1.2 MW): 5 K 8 K 800 s no beam 8 K 5 K

800s 8s Pulsed UCN source

800s 8s Pulsed UCN source

800s 8s Pulsed UCN source

UCN cold source cold source h = 2.5 m V = 2m 3 v = 5 – 9 m/s v = 0 – 7 m/s a b Coherent strong interaction surface potential of solid deuterium (106 neV 4.5 m/s) Cu Be, DLC Needs: storage volume coating ( storable neutrons ~v c 3 !)

low wall loss probability µ long storage time high Fermi potential more UCN (v 3 ) Al Pb Ni C Diamond BeO Be 300 K Be 70 K 58 Ni 65 Cu CuFe DLC Storage materials

Detector count rate: B Sample Magnet UCN from ILL-turbine Detector B % time [s] wall material: loss and depolarization

Wall loss coefficient [1 / wall collision] x DLC is a good choice also for (DLC)=110 -6, (Be)= Diamondlike carbon F. Atchison et al., Phys. Lett. B 625, 19 (2005). T. Brys et al., Nucl. Instr. and Meth. in Phys. Res. A 550, 637 (2005).

UCN transmission: Fermi potential v c (Be) = ( ) m/s v c (DLC) = ( ) m/s F. Atchison et al., NIMB 260, 647 (2007), Phys. Lett. B 642, 24 (2006).

DLC: (6.9 ± 0.2)m/s F. Atchison et al., NIMB 260, 647 (2007). PLB 642, 24 (2006). Be: (6.8 ± 0.2)m/s UCN transmission: Fermi potential

Need to know for solid Deuterium: UCN production cross section –theoretical: Golub and Böning, ZPB51(1983)95 –experimental: F. Atchison et al., PRC 71, (2005). UCN lifetime –theoretical: Liu et al., PRB62(2000)R3581 –experimental: Morris et al., PRL89(2002) UCN mean free path –theoretical: incoherent cross section, inc = 4.1 barn –experimental: F. Atchison et al., PRL 95, (2005). solid D 2 : Motivation

~ 30ms v = 5 m/s = 150 mm / 30 ms h ~ 150mm R mfp, solid D 2 : Motivation

1000 – 100 m/s100 – 10 m/s 10 – 0 m/s cold very-cold ultra-cold Transmission experiments UCN, VCN

Liquid Solid 12 hours Preparation of sD 2 (T = 18 K)

Thermal stress

Thermal stress IV Mean free path 1 cm 2 cm 8 cm Cross sections UCN F. Atchison et al., PRL 95, (2005).

CN sD 2 UCN + CN Detector UCN UCN production at SINQ, PSI F.Atchison et al., PRC 71, (2005).

Empty cell liquid D 2 and gaseous D 2 solidD 2 UCN production at SINQ, PSI F. Atchison et al., PRC 71, (2005).

Our experiment: F.Atchison et al., PRC 71, (2005). R solid,8K = (1.11±0.23) x cm -1 – in agreement with Z.-Ch. Yu et al., ZPB62(1986)137 Estimate for PSI UCN source: CN ~ 2 x cm -2 s -1 mA UCN ~ 30 ms –50% of equilibrium density after 4s proton pulse UCN = R solid,8K x CN x UCN x cm cm -3 in storage, 1000cm -3 in experiments In Grenoble: ρ(UCN) = 10 UCN cm –3 UCN production at PSI

Ring cyclotron: 600MeV, 2mA 1.2MW (unique!) Where is the UCN source UCN Source nEDM experiment

Proton beam

Proton beam line Proton beam 1000 A (10 ms) test beam September 6, 2007 UCN source

1.2 MW proton beam, UCN source, Exp. Areas EDM > 1000 UCN/cm 3 n target Test beam 1000 A, 10 ms September 6, 2007 Experimental areas

test beam dump

Harp monitors Quadrupole collimatorD 2 O circuit Proton beam Experimental floor Existing

Proton beam line Proton beam

PSI UCN source spallation target 1.2 MW p beam 2.5 m 2m 3 Cold source Relative Masses: Flat foil 100 % Torus 110 % Dome 131 % 50 cm Torus Dome

UCN tank fabrication

Vacuum box of UCN tank system

spallation target target head iron shielding lead block target water pipes

D 2 Gas System He liquefier D 2 hut D 2 tanks 30 m 3

Gas handling boxes

UCN-Tanksystem: Schwerwasser 8m 3 D 2 O-Tanks Pumpe (25 l/s) Heat exchangers Ion exchangers

Papers in 2003/04 1)Ortho-para equilibrium in a liquid D 2 neutron moderator under irradiation PRB 68, (2003). 2)Spallation yields of neutrons produced in thick lead/bismuth targets by protons at incident energies of 420 and 590 MeV NIMB 217, 202 (2004). 3)An apparatus for the investigation of solid D 2 with respect to ultra-cold neutron sources NIMA 533, 491 (2004).

Papers in ) The simulation of ultracold neutron experiments using GEANT4 NIMA 552, 513 (2005). 2) On the use of lead/tin alloys as target material for the production of spallation neutrons NIMA 539, 646 (2005) 3) A fast kicker magnet for the PSI 600 MeV proton beam to the PSI ultracold neutron source NIMA 541, 598 (2005) 4) Magnetron sputtered Be coatings as reflectors for ultracold neutrons NIMA 551, 429 (2005). 5) Measured Total Cross Sections of Slow Neutrons Scattered by Gaseous and Liquid 2 H 2 PRL 94, (2005) 6) Production of ultracold neutrons from a cold neutron beam on a 2 H 2 target PRC 71, (2005) 7) Magnetic field stabilization for magnetically shielded volumes by external field coils NIMA 554, 527 (2005). 8) A novel apparatus for the investigation of material properties for the storage of ultracold neutrons NIMA 550, 637 (2005)

Papers in 2005/06/07 1)First storage of ultracold neutrons using foils coated with diamond-like carbon Phys. Lett. B 625, 19 (2005). 2)Measured total cross sections of slow neutrons scattered by solid deuterium and implications for ultracold neutron sources Phys. Rev. Lett. 95, (2005). 3) Storage of ultracold neutrons in a volume coated with diamondlike carbon Phys. Rev. C 74, (2006). 4) Diamondlike carbon can replace beryllium in physics with ultracold neutrons Phys. Lett. B 642, 24 (2006). 5) The spallation target of the ultra-cold neutron source UCN at PSI NIMA 564, 51 (2006). 6) A time-of-flight chopper for ultracold neutrons NIMA, 557, 572 (2006). 7) Structural characterization of diamond-like carbon films for ultracold neutron applications Diamond & Related Materials, 16, 334 (2007). 8) Measurement of the Fermi potential of diamondlike carbon and other materials NIMB 260, 647 (2007).

On the way to the top! Schedule: 1 st UCN October 2008

PSI UCN source heavy water moderator 2.5 m 2m 3 Lifetime in D 2 O: 5 ms v = 2200 m/s Range: ~10 m

PSI UCN source heavy water moderator 2.5 m 2m 3 Lebensdauer in D 2 O: 5 ms v = 2200 m/s Reichweite: ~10 m

spallation target target head iron shielding lead block target water pipes

target construction

target head lead block water pipes

iron shielding block target construction

Detector count rate: B Sample Magnet UCN from ILL-turbine Detector B % time [s] wall material: loss and depolarization

Detector count rate: B Sample Magnet UCN from ILL-turbine Detector B % time [s] wall material: loss and depolarization